In recent years, a semiconductor device for power is getting more widely used not only for general industrial use and electric railroad use but also for on-vehicle use as environment consciousness increases. In particular, reduction in size and weight of each of on-vehicle parts in a limited allowable size is directly linked to the performance of the vehicle, and therefore on-vehicle parts tend to be decreased in size also for a semiconductor device for power.
Such a semiconductor device has a semiconductor element for power mounted, for example, on a die pad of a DBC (Direct Bonded Copper: registered trademark) via a high-lead solder high in heat resistance.
However, the use of harmful substance containing lead comes to be restricted, and making lead-free is demanded.
Hence, as a lead-free jointing material high in heat resistance other than the high-lead solder, a joining method using sintered-type silver paste of joining a silver filler of a nano-order at a temperature of a melting point or lower is under review. The sintered-type silver paste is high in thermal conduction and is effective for joining the semiconductor element for power handling large current.
For example, there are suggested a method for joining a semiconductor element and a DBC substrate by a porous metallic film (refer to US-A1 2013/0256894) and a method for transferring film-shaped silver paste formed by pre-drying printed silver paste to a semiconductor element and then joining it to a DBC substrate (refer to JP-A 2014-503936).